Turning machines, such as lathes, are widely used to manufacture parts from work-pieces of various shapes (cross section). Modern CNC lathes allow rapid and automated production of machined parts. They normally feed such a work-piece through a hollow spindle that rotates with an associated lathe chuck; and is located behind the chuck. This allows a rotating work piece to be progressively (intermittently) advanced through the chuck towards the lathe cutting tools. When the machine is used to cut a work-piece having a diameter that is only slightly smaller than the inner diameter of the spindle, the work-piece is in-part supported by the spindle. However, if the diameter of the work-piece is significantly smaller than the inner diameter of the spindle, the work-piece may be substantially unsupported along the length of the spindle and may be subjected to bending as a result of centrifugal forces, which cause a whipping and/or vibration (with noise) of the unsupported length of the work-piece. This makes it difficult to machine properly and to meet the required tolerances. Modern lathes, capable of operating at very high RPM rates (typically 5000-10000 RPM) may, disadvantageously, have to be run at lower than preferred speeds to obviate such problems.
The problem of adequately supporting and machining the work-piece in turning machines, during such operations has been addressed by the use of spindle liners (also referred to as filler tubes or reduction tubes), which are widely used to support a work-piece in machine spindles. Spindle liners are typically tubular in configuration; often comprising a series of connected pipe sections and flanges with an outer diameter sized for a close slip-fit within the machine spindle. Typically, they have portions with an inner diameter sized to provide a fairly close (within 0.3 to 0.6 mm) fit for the work-piece to ensure material travels through Spindle liner/reduction tube/bushings if the material is bent or deviates in cross section. Reducing the clearance below 0.3 mm requires the use of relatively expensive, ground/bright work-piece material manufactured to tighter tolerance of diameter and straightness.
Even with such liners vibration of the work piece can be a problem as the work-piece is not evenly supported; for example, small diameter work-pieces typically flex and whip to boundaries of spindle liner reduction tube/bushing; causing damage to the spindle liner, leading also to work-piece material being scrapped as a result of damage. Vibration of the entire work-piece becomes more of an issue as the diameter/length of material increases (therefore the mass of material increases to be contained). All of these problems are typically reduced by limiting machining speed; however, this adversely affects the attainment of required manufacturing tolerances.